1. Field of the Invention
The present invention relates to torque coupling assemblies in general, and more particularly to a hydraulic fluid plenum plate assembly in a hydraulically actuated torque coupling assembly for providing hydraulic fluid from a hydraulic fluid reservoir to a hydraulic fluid pump of the torque coupling assembly.
2. Description of the Prior Art
Many hydraulically actuated torque coupling assemblies, such as motor vehicle limited slip differentials, employ an internal hydraulic pump to convert the spin speed difference between one of output shafts and a differential case to a hydraulic pressure that actuates a piston actuator, which in turn activates a multi-plate friction clutch assembly. As illustrated in FIG. 1, a pickup tube 110 draws a hydraulic fluid from an axle sump by a vacuum generated by the hydraulic pump and transports the hydraulic fluid to a hydraulic plenum chamber 112 disposed between a plenum plate 114 and the differential case 116 adjacent to the hydraulic pump through an inlet port 118 fluidly connecting the plenum chamber 112 with the hydraulic pump. An inlet end of the pickup tube 110 is provided with an inlet opening 120 submerged in the hydraulic lubricant fluid in the axle sump, while an outlet end of the pickup tube 110 is provided with an outlet opening 122 through the plenum plate 114 fluidly connecting the pickup tube 110 with the plenum chamber 112. An outlet port through which the hydraulic fluid exits the differential case 12 is depicted with the reference numeral 126.
As shown in FIG. 1, the outlet opening 122 of the prior pickup tube 110 is positioned at the middle height of the plenum chamber 112. In other words, a fluid level 124 in the plenum chamber 112 is substantially lower of the inlet port 118 of the hydraulic pump at an uppermost angular position thereof relative to a central axis 126. As the differential case 116 rotates, the inlet port 118 of the hydraulic pump is positioned in and out of the hydraulic fluid in the plenum chamber 112. As a result, air bubbles could be sucked in through the inlet port 118 and entrapped into the hydraulic pump and the piston actuator. In addition, it would take a time for the plenum chamber 112 to be fully filled with the hydraulic fluid by the continued pumping action of the hydraulic pump. In other words, the prior art plenum chamber arrangement poses the problem of air bubble entrapment and the time delay.
Therefore, the hydraulically actuated torque coupling assemblies of the prior art having plenum chambers, including but not limited to those discussed above, are susceptible to improvements that may enhance their performance and cost. With this in mind, a need exists to develop an improved hydraulically actuated torque coupling assembly that is compact in size, can be packaged into existing torque coupling assemblies, and greatly reduces the air bubble entrapment and the time delay problems, thus advancing the art.